Electrocoagulation - Overview of the Technology

Coagulation is a critical physio-chemical operation used in water treatment. This is a process used to cause the destabilization and subsequent aggregation of smaller particles into larger complexes. Water contaminants such as ions (heavy metals) and colloids (organic and inorganic) are primarily held in solution by electrical charges. Colloidal systems could be destabilized by the addition of ions of the charge opposite to that of the colloid. The destabilized colloids can then aggregate and subsequently be separated from the wastewater.

Coagulation can be achieved by both the chemical or electrical means. Chemical coagulation has been used for decades to destabilize suspensions and to effect precipitation of soluble species and other pollutants from aqueous streams. Alum, lime and polymers are some of the chemical coagulants used. These processes, however, tend to generate large volumes of sludge with high bound water content which can be difficult to separate and dewater. The processes also tend to increase the total dissolved solids content of the effluent, making it unacceptable for reuse within industrial applications. Other aspects of chemical coagulation are also becoming increasingly less acceptable. The disposal cost of the large volumes of sludge (generally of fairly high hazardous waste category), the cost of the chemicals required to achieve coagulation and the environmental issues associated with the process are critical problems in many industries.

Electrocoagulation, the passing of the electrical current through water, has proven very effective in the removal of contaminants from water. Although the electrocoagulation mechanism resembles the chemical coagulation - the cationic species being responsible for the neutralization of surface charges - in many ways it is very different. Electrocoagulation is a process of destabilizing suspended, emulsified or dissolved contaminants in an aqueous medium by introducing electrical current into the medium. The electrical current provides the electromotive force causing the chemical reactions.

Several distinct electrochemical processes occur during the electrocoagulation process independently.

Processes occurring:

Seeding resulting from the anode reduction of metal ions that become new centers for larger, stable, insoluble complexes.

Emulsion breaking resulting from oxygen and hydrogen ions reacting with emulsified substances and forming water insoluble material.

Halogen completing - as the metal ions bind themselves to halogens resulting in formation of large insoluble complexes and isolating pesticides, herbicides, chlorinated PCBs, etc..

Bleaching by oxygen species produced in the reaction chamber and providing oxidisation of chemical substances and also reducing bio-hazards through oxidisation of bacteria, viruses, etc..

Electron flooding of the water affects the polarity of water, allowing colloidal materials to precipitate.

The electrons create osmotic pressure rupturing cell walls of bacteria, cysts, and viruses. Oxidation and reduction reactions are forced to their natural end point. Electrocoagulation can speed up the natural processes occurring in wet chemistry Electrocoagulation induced pH typically shifts towards neutral. The principal cathodic reaction is the reduction of hydrogen ions to hydrogen gas (2H+ + 2e- = H2). The principal anodic reaction is the release of metal ions into solution (eg. 3Al = Al3+ + 3e-). The anodes are sacrificed during the process.

The wastewater passes through a chamber with the cathodes and anodes. The electrical current is introduced via parallel plates constructed of metals selected to optimise the removal process. The two most common plate materials are iron and aluminium. In accordance with the Faraday's Law, the metal electrodes are sacrificed and slowly dissolve into the liquid medium. The metal ions tend to form metal oxides that electromechanically attract the destabilized contaminants. After the treated wastewater leaves the electrocoagulation chamber, the destabilized colloids are allowed to flocculate and then separated in an integrated system. The sludge can be further de-watered using a filter press, settling pond, or other de-watering techniques.

System Capabilities:

Removes heavy metals;

Removes suspended and colloidal solids;

Destabilizes oil and other emulsions;

Removes fats, oils and grease;

Removes complex organics; and Destroys and reduces bacteria, viruses and cysts.

Benefits:

Treats multiple contaminants;

Sludge minimization;

Capital cost significantly less than conservative technologies;

Operating cost significantly less than conservative technologies;

Low power requirements;

Low maintenance;

Minimal operator attention;

Consistent and reliable results.

Please contacct ForeverPure for detailed information.